1. Field of the Invention
The present invention relates to an optical waveguide plate of a surface light emitting apparatus used for spreading light from a light source over the entire light emitting surface and emitting the light.
2. Description of the Related Art
Such surface light emitting apparatus have recently been used as the light source for backlight of a liquid crystal display, that outputs light from a point source such as LED chip by spreading the light over a plane. In the surface light emitting apparatus, light emitted by one or more light emitting diode enters through one end of an optical waveguide plate that has opposing principal planes, and exits through the whole area of the other principal plane of the waveguide.
The surface light emitting apparatus has such a constitution as shown in a plan view of FIG. 20, comprising a casing 903, an optical waveguide plate 901 made of a transparent resin that has a first principal plane and a second principal plane, a light emitting diode 902 mounted so as to oppose the end face of the optical waveguide plate 901, and a reflector (not shown) mounted on the second principal plane of the optical waveguide plate, so that light emitted by the light emitting diode 902 is output through the entire area of one principal plane of the optical waveguide plate 901.
In the surface light emitting apparatus having the constitution described above, since light emitted by the light emitting diode 902 is attenuated while being transmitted through the optical waveguide plate 901, with the light intensity decreasing in inverse proportion to the distance from the light source, a light diffusion dot pattern is formed on the second principal plane that serves as the reflector so as to obtain light output uniformly distributed over the plane. The light diffusion dot pattern makes the luminance distribution uniform over the light emitting surface by increasing the density of dots or the area of each dot with the distance from the light source, thereby increasing the area occupied by the light diffusing dots.
FIG. 21 is a plan view showing a light diffusion dot pattern of a reflecting surface of the optical waveguide plate disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 8-271893. In this example, the area of each of dots 102 is increased with the distance from a light source 101, thereby gradually increasing the proportion of area occupied by the light diffusing dots as the distance from the light source increases.
With the light diffusion dot pattern of the prior art shown in FIG. 21, however, there has been the problem of a bright line generated due to the arrangement of the light diffusing dots.